Just because a category is not updated does not necessarily mean that the web sites listed in the category are not useful information.
Also, please remember that for categories with subcats, the update date on the higher level category doesn't indicate whether any changes were made to a subcat. Getting rid of a cat means getting rid of all subcats too, after all.
That's not to say that we don't get rid of categories that are no longer useful - when there are no web sites in existence on a subject, and for one reason or another, it is obvious that there won't be any more, a category will get deleted. That is a pretty rare occurrence, though.